Sapiński, Bogdan
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inżynieria mechaniczna
automatyka, elektronika, elektrotechnika i technologie kosmiczne
automatyka, elektronika, elektrotechnika i technologie kosmiczne
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Item type:Article, Access status: Open Access , Magnetorheological fluids subjected to non-uniform magnetic fields: experimental characterization(2023) Kubık, Michał; Gołdasz, Janusz; Macháček, Ondřej; Strecker, Zbyněk; Sapiński, BogdanMagnetorheological (MR) fluids are suspensions of fine, low-coercivity, high magnetizable particles in a continuous liquid phase. When subjected to magnetic field, the material exhibits a rapid change in the apparent viscosity of several orders of magnitude. This unique capability has been successfully exploited in automotive semi-active suspensions systems or systems for manufacturing high quality optics. In a majority of the existing systems, the rheology of MR fluids is controlled by an external uniform field oriented perpendicularly to the fluid flow direction. In general, it is an inherent feature of MR systems operating in flow, shear or squeeze modes, respectively. There is an experimental evidence that the behavior of MR fluids in the so-called pinch-mode (in which the fluid is subjected to non-uniform magnetic field distributions ) clearly stands out against the remaining three operating modes. With the predecessors, the flow through the channel occurs once a pressure across it exceeds the field-dependent threshold pressure. For comparison, in pinch mode valves the magnetic flux energizes mostly the layers of the materials near the channel walls. The outcome is a change in the channel’s effective diameter achieved solely via material means without changing its geometry. To study the fluid’s unique behavior in the pinch mode, the authors designed a prototype valve assembly and examined several fluid formulations of various particle concentration levels across a wide range of external (velocity, magnetic field density) stimuli in an organized effort to further comprehend the phenomenon. The obtained data indicate that the magnitude of the particular effect does not only depend on the magnitudes of the magnetic stimuli but also on the particle concentration; the smaller the concentration of particles the more pronounced the pitch mode like behavior is. In general, the authors believe that the study may provide guidelines as to the selection of fluid formulations for developing novel valveless actuators utilizing MR fluids operating in pinch mode.Item type:Article, Access status: Open Access , Experiments and analysis of the limit stresses of a magnetorheological fluid(2022) Horak, Wojciech; Stępień, Barbara Iwona; Sapiński, Bogdan
Wydział Inżynierii Mechanicznej i RobotykiThis paper presents the results of a rheological test of a commercial magnetorheological (MR) fluid (MRF-132DG). The research includes the problem of measuring and interpreting limit stresses under conditions close to the magnetic saturation of the fluid. Four different limit stresses were determined, two related to the yield point and two related to the flow point. Methods for determining limit stresses, especially due to excitation conditions, were also analysed. The aim of this study is to determine the effect of selected parameters on the values of limit stresses of the selected MR fluid. An additional objective is to highlight the problems of defining and interpreting individual limit stresses in MR fluids, particularly in the context of selecting the values of these stresses for the purpose of modeling systems with MR fluids.Item type:Article, Access status: Open Access , Pinch mode magnetorheological flow bench: fluid flow analysis(2023) Gołdasz, Janusz; Sapiński, Bogdan; Kubik, Michał; Machacek, Ondras; Bańkosz, Wojciech
Wydział Inżynierii Mechanicznej i RobotykiMagnetorheological (MR) fluids are known smart materials. In the presence of magnetic field the material develops a yield stress. The technology has been used in the automotive industry, for example, or high quality optical finishing applications. In the (existing) conventional flow-mode valves the MR fluid is energized by magnetic flux perpendicular to the fluid flow path. The effect is an increase in the material’s effective resistance-to-flow. The so-called gradient pinch mode (GPM) follows a different principle – the flux in the flow channel is directed to activate the fluid in the areas adjacent to the channel walls. Then, high yield stresses are induced in the material in the adjacent zones and low yield stresses are achieved in the middle of the channel, the yield stress distribution is non-uniform. As a result, a Venturi-like contraction is formed solely by material means, i.e. without changing the flow path geometry. This may lead to a new category of controlled semi-active valves. However, a fundamental research is still required to characterize the rheology of MR fluids in this mode. In the study the authors explore opportunities for building a pinch mode valve assembly for the experimental work with MR fluids. The authors propose a solenoid assembly that can be integrated into a flow bench, and then proceed with a CFD steady-state study of the fluid flow through the valve. The results are then presented in the form of velocity plots and pressure maps as well as averaged pressure drop vs volumetric flow rate, respectively, at various levels of ampere turns.